1. Field of the Invention
The present invention relates, in general, to a method for preparing a ketone and, more particularly, to a method for preparing a ketone by use of aldehyde and olefins as starting materials in the presence of a transition metal catalyst.
2. Description of Related Art
Until recently, the introduction of carbonyl, one of the most important organic groups, into organic compounds has been in extensive study for preparing ketones. In one of the most typical methods, aldehyde is reacted with a nucleophilic organic metal compound, such as alkylmagnesium halide, to give secondary alcohol which is then oxidized into ketone with the aid of various oxidizers. However, this method suffers from several disadvantages: it must pass through many reaction steps and produces many unnecessary by-products during the reaction steps.
In an effort to avoid these problems, active research has been directed to hydroacylation techniques of preparing ketones directly from olefins and aldehyde by use of metal catalysts. Conventional hydroacylation techniques have the disadvantage of easily causing side-reactions, such as a formation of alkane from aldehyde through decarbonylation. So, in order to suppress such decarbonylation, a technique for introducing carbon monoxide or ethylene gas under high pressure is known, but has disadvantages of using gas of high pressure and vigorous reaction conditions. Alternatively, a hydroacylation technique for synthesizing ketones from benzaldehyde and vinyl silane at room temperature by use of a cobalt catalyst is reported, however, this technique is disadvantageous in terms of low feasibility, because usable olefins are defined in vinyl silane or its derivatives. A recent hydroacylation technique, capable of being conducted under relatively simple and mild conditions, synthesizes ketones by introducing a transition metal catalyst and 2-aminopyridine derivatives as additives, in addition to aldehyde and olefin, as illustrated in the following chemical reaction formula 1. 
The above reaction is specifically shown in chemical reaction formula 2, below. 
As illustrated in said reaction formula, aldimine 1 resulting from a reaction of aldehyde with a 2-aminopyridine derivative, is reacted with a metal catalyst to form a metal hydride 2, which is then reacted with olefin to afford ketimine with the aid of an alkyl metal compound 3. Then, ketimine 4 is hydrolyzed with water to produce ketone.
Though conducted under simple and mild conditions, this method suffers from the disadvantages of using 10 mol % metal catalysts and 20 mol % 2-aminopyridine derivatives as catalysts useful in the reaction, and heating the reactants for 60 hours or more in order to obtain ketone with high yields of 80% or higher.
Leading to the present invention, thorough and intensive research on the synthesis of ketones, repeated by the present invention aiming to efficiently improve a reaction by use of a 2-aminopyridine derivative and a transition metal catalyst among the preparation of ketones through a reaction of aldehyde with olefins (hydroacylation), resulted in the finding that addition of acids and primary amines can increase efficiency of the catalyst not only to improve the yields of ketones but also to reduce the time of the reaction.
Therefore, it is an object of the present invention to overcome the above problems encountered in the prior art and to provide a method for preparing a ketone with high yields.
The present invention is directed to the synthesis of ketones by reacting aldehyde with olefins in the presence of catalysts and additives. A transition metal catalyst, a 2-aminopyridine derivative, amines and acids, useful as catalysts and additives, are reacted together to prepare ketones, as illustrated in the following chemical reaction formula 3: 
Useful as starting materials in the present invention are aldehyde and olefins. As aldehyde, all aldehydes such as an aromatic or aliphatic aldehyde can be used, and as olefins, use can be made of not only ethylene but also almost all vinyl-containing olefins having an aliphatic or aromatic alkyl moiety. Examples of transition metal catalysts suitable for the preparation of ketones include Wilkins catalysts such as (PPh3)3 RhCl, rhodium monovalent catalysts such as [Rh(C8H14)2Cl]2, and rhodium trivalent catalyst such as [RhCl3AH2O]. When rhodium monovalent or trivalent catalyst is employed, various phosphine compounds, such as triphenyl phosphine (PPh3), are preferably added together. Transition metal compounds, such as ruthenium or iridium, may be used as catalysts, but have inferior reactivity to rhodium compounds.
In combination with the transition metal catalyst, a 2-aminopyridine derivative is used according to the present invention. A variety of 2-aminopyridine derivatives may be used as additional catalysts. In primary amines, most aromatic and aliphatic amines, including aniline, benzylamine, cyclohexylamine, and tert-butylamine, may be used. As for acids, various aromatic and aliphatic acids include, but are not limited to, benzoic acid, acetic acid, and p-toluene sulfonic acid.
A suitable organic solvent, if not indispensable for the synthesis, is helpful in increasing the efficiency of the catalysts or additives.
In the synthesis of ketones according to the present invention, the reactants are reacted in the reaction mechanism shown in the following chemical reaction formula 4: 
As shown in the above chemical reaction formula, the reaction starts with the formation of aldimine 5 through the condensation of aldehyde with aniline. Then, a different aldimine 1 is formed through a transimination of aldimine 5 with 2-amino-3-picoline, followed by reacting with a transition metal catalyst to afford a metal hydride 2, which is then reacted with 1-hexene with the aid of alkyl metal compound 3 to produce ketimine 4. This ketimine is hydrolyzed by water to form ketone, or reacted with aniline through transimination to form a different ketimine which is then hydrolyzed by water to produce ketones. Aniline plays a role in easing production of aldimine 1 through combination of 2-amino-3-picoline with aldehyde, an important intermediate of reaction substrates. A formation of aldimine 1 through a reaction of transimination from aldimine 5 resulting from aniline and aldehyde is faster than a direct formation of aldimine 1 from aldehyde and 2-amino-3-picoline. Acids useful as the additives are responsible for easily carrying out the condensation or transimination. Therefore, the hydroacylation using two such additives, namely aniline and acids, in the present invention has a much higher reaction efficiency and faster reaction time than hydroacylation by use of known Rh(I) compounds and 2-amino-3-picoline.
A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.